The air humidity of the fresh air that is delivered to an internal combustion engine as part of the fuel mixture influences the combustion process. Here the water vapor admixed by means of the air humidity reduces the combustion temperature, whereby in particular fewer harmful and unwanted nitrogen oxides occur. For this reason there is a desire to measure the relative air humidity of the fresh air in order to be able to model and, if appropriate, to control the quantities of contaminants occurring during the combustion process. If the relative air humidity is known, the effect of systems for contaminant reduction and Exhaust Gas Recirculation (EGR), Lean NOx Traps (LNT) or Selective Catalytic Reduction (SCR) is detected or such systems can be controlled for improved efficiency. Such a method for the operation of an internal combustion engine is known, e.g. from DE 10 2007 053 719 B3. As with DE 198 31 748 A1, which is concerned with a similar problem, a humidity sensor is used.
But here there is the problem that the relative air humidity is relatively difficult to measure accurately and with a small delay over the great range of the fluctuation of temperatures that can occur in a fresh air induction tube.
Accordingly, a method for the measurement of relative air humidity in a fresh air induction tube of an internal combustion engine is provided. The method comprises measuring a concentration of oxygen in the fresh air induction tube by an oxygen sensor, determining a temperature in the fresh air induction tube, and determining the relative air humidity depending on the measured concentration of oxygen and the determined temperature.
The disclosures based on the knowledge that the relative air humidity can be measured indirectly using an oxygen sensor. Here the deviation of the measured concentration of oxygen from the nominal value of about 21 percent for normal ambient air is determined and the relative air humidity is determined using the likewise determined temperature occurring in the fresh air induction tube.
By means of said indirect measurement of the relative air humidity, the method according to the disclosure enables a simple and accurate measurement of the relative air humidity, without having to use the separate sensor provided for this purpose in the previous systems.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.